Motion vector correction circuit and method

ABSTRACT

It is determined whether each block ( 51 ) including a plurality of pixels extracted from a basic field ( 30 ) has an edge or not, and then which state, stationary or non-stationary, each of the pixels forming together the block ( 51 ) determined to have an edge is. There is calculated an absolute value of a difference between a pixel determined to be non-stationary and a pixel ( 91  or  92 ) in each pixel position in a reference field ( 40 ) or pixels ( 82  to  85 ) included in the reference field and adjacent to the non-stationary pixel, and a correlation is found between such pixels in consideration according to the calculated difference absolute-value. A motion vector is determined by the block matching method according to results of the determination, and allocated to each of the pixels. Thus, the motion vector of each block is corrected to an accurate one of each of the pixels.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a motion vectorcorrection circuit and method, and more particularly to a circuit for,and a method of, correcting a motion vector determined by the blockmatching method.

[0003] This application claims the priority of the Japanese PatentApplication No. 2002-145265 filed on May 20, 2002, the entirety of whichis incorporated by reference herein.

[0004] 2. Description of the Related Art

[0005] Heretofore, the TV broadcasting systems have adopted most widelythe interlaced scanning or interlacing in which the electron beam isscanned across the screen once every other horizontal scan line. In theinterlacing, a field image formed from odd scan lines and a one formedfrom even scan lines, form together one frame image. An image interlacedwith a low frequency incurs a flicker in screen (will be referred to as“screen flicker” hereunder) which will degrade the on-screen imagequality.

[0006] Also, the interlacing is adopted as the television standard overthe world. For example, the PAL (phase alternation by line) system isone of such television standards, prevailing in the European countries.In the PAL system, the field frequency is 50 Hz (a frame image is formedfrom 25 frames/sec and a field image is formed from 50 fields/sec).

[0007] More specifically, to suppress the screen flicker, the PAL systemhas adopted the field frequency doubling technique which converts afield frequency of 50 Hz into a one of 100 Hz by interpolating orotherwise processing an input image signal.

[0008]FIG. 1 shows a block diagram of a field frequency doubler circuit5 having the field frequency doubling technique applied therein. Asshown, the field frequency doubler circuit 5 is formed integrally in atelevision receiver 6 including an input terminal 64,horizontal/vertical deflection circuit 65 and a CRT 63. The fieldfrequency doubler circuit 5 includes a frequency-doubling converter 55and a frame memory 52.

[0009] The frequency-doubling converter 55 is supplied with a PAL-basedimage signal of 50 fields/sec from the input terminal 61 and writes thesignal to the frame memory 52. The frequency-doubling converter 55 readsthe image signal from the frame memory 52 at a speed double that atwhich the image signal was written. Thus, it is possible to double thefrequency of the 50-fields/sec image signal and produce a 100-fields/secimage signal.

[0010] The frequency-doubling converter 55 supplies thefrequency-doubled image signal to the CRT 63. The CRT 63 will displaythe supplied image signal on a screen thereof. It should be noted thatin the CRT 63, the horizontal and vertical deflection of the imagesignal is controlled according to a horizontal/vertical sawtooth wave ofthe frequency double that of the input image signal, produced by thehorizontal/vertical deflection circuit 62.

[0011]FIGS. 2A and 2B show the relation between each field and pixelposition before and after subjected to the frequency-doublingconversion. In FIGS. 2A and 2B, the horizontal axis indicates a time andthe vertical axis indicates a vertical position of a pixel. Also, thesmall blank circle in FIG. 2A indicates an interlaced image signal of 50fields/sec before subjected to the frequency-doubling conversion, andthe small hatched circle in FIG. 2B indicates an interlaced image-signalof 100 fields/sec after subjected to the frequency-doubling conversion.

[0012] In the image signal shown in FIG. 2A, fields f1 and field f2 aresignals produced from the same frame in a film, and similarly, fields f3and f4 are signals produced from the frame. Since these image signalsare interlaced ones, adjacent fields are different in vertical pixelposition from each other. Thus, a new field cannot be produced betweenfields while maintaining the interlaced state.

[0013] On this account, two fields f2′ and f1′ are newly producedbetween the fields f1 and f2, and two fields f4′ and f3′ are producedbetween the fields f3 and f4 with no fields being produced between thefields f2 and f3, as shown in FIG. 2B. Say, one frame is formed fromfour fields, namely, two frames.

[0014] Each of the newly formed fields f1′, f2′, . . . may have its ownpixel value determined as a mean value, respectively, of three-pixelssurrounding that pixel by a median filter or the like in some cases.Also, the new fields f1′, f2′, . . . will have the same contents as thefields f1, f2, . . . , respectively.

[0015] That is, the field frequency doubler circuit 5 can increase thenumber of images per unit time and thus suppress the aforementionedscreen flicker by producing two new fields and no new fields alternatelybetween fields of an: image signal before subjected to thefrequency-doubling conversion.

[0016]FIG. 3A shows the relation between each field and image positionwith a television signal (will be referred to as “TV signal”hereinafter) being not yet subjected to the frequency-doublingconversion when the image moves horizontally. As shown in FIG. 3A, sincethe fields f1, f2, f3, . . . belong to independent frames, respectively,the image will appear in another position. The image will movehorizontally (to the right) each time it shifts from the field f1 to thefield f2, f3 . . . .

[0017] By doubling the frequency of the image signal in the TV signalshown in FIG. 3A by the field frequency doubling technique, the sameimage will appear in the same position when the fields f1 and f2′ formtogether the same frame as shown in FIG. 3B. Similarly, with the fieldsf1′ and f2 forming together the same frame, the same image appears inthe same position.

[0018] Note that since an output image signal regularly forms each fieldin a 1/100-sec cycle, the image-moving time zone is shorter than theimage-stationary time zone and thus the image motion actually appearsdiscontinuous when it is viewed on a CRT. A typical example of theconventional solutions to this “discontinuous image motion” problem isto break an image into blocks, each including a predetermined number ofpixels, and determine the similarity between the blocks by the blockmatching method, for example, in order to determine a motion vector andcorrect the image motion by shifting pixel positions in each of theblocks according to the motion vector thus determined.

[0019] Note the block matching method is a technique to break a basicfield 80 into a plurality of basic blocks 101, detect a block mostsimilar to the basic blocks 101 in the basic field 80 from a searchblock 103 moved within a search range 104 in a reference field 90, andtake, as a motion vector, a positional deviation (in direction andmagnitude of a motion) between the detected search block 103 and basicblock 101, as shown in FIG. 4.

[0020] For determination of the above similarity, a difference of eachpixel value of the search block 103 from a pixel value corresponding tothe basic block 101 is determined, and then an assessment value sumrepresented by the difference, for example, a difference absolute-valuesum, is determined. Next, this procedure is repeated for all the searchblocks 103, and a minimum one is determined of assessment value sums,that is, difference value sums. The search block 103 showing the minimumdifference sum is taken as showing the highest similarity to the basicblock 101, and a vector that can be determined between a pixel at theorigin of such a block and a pixel at the origin of the basic block 101is taken as a motion vector.

[0021]FIG. 5 shows a motion correction circuit 7 which uses the blockmatching method to make motion correction of an image signal having thefrequency thereof doubled by the field frequency doubler circuit 5.

[0022] As shown, the motion correction circuit 7 includes an imagememory 71, motion vector detector 72 and an image shifter 73.

[0023] The image memory 71 is sequentially supplied with interlacedimage signals having been doubled in frequency by the aforementionedfield frequency doubler circuit 5 and one frame of which is composed offour fields each having a field frequency of 100 fields/sec. The imagememory 71 will store the supplied image signals in units of a field forone frame. Say, an image signal outputted from the image memory 71 willhave a one-frame delay in relation to an image signal supplied to theimage memory 71.

[0024] The motion vector detector 72 is sequentially supplied with thebasic fields 80 for supply to the image memory 71 and with the referencefields 90 supplied from the image memory 71 and delayed one frame inrelation to the basic field 80. The motion vector detector 72 extractsthe basic block 101 from the basic field 80, and the search block 103from the reference field 90, and determines a motion vector by the blockmatching method. The motion vector detector 72 sends the motion vectordetected at each pixel or block to the image shifter 73.

[0025] The image shifter 73 is supplied with the image signal delayedone frame in relation the input image signal from the image memory 71.The image shifter 73 receives the motion vector from the motion vectordetector 72. Also, the image shifter 73 shifts each block of thesupplied image signal within the range of the received motion vector andin the direction of a motion vector, and supplies the blocks thusshifted to a CRT 74.

[0026] However, the conventional motion correction circuit. 7 adoptingthe block matching method forms one block from so many pixels as 16×4pixels for example in order to minimize the load to the entire circuitby reducing the operational amount. Within the block formed from suchmany pixels, pixels actually move differently from each other. In such acase, if an image is shifted in blocks by the image shifter 73 in thedirection of a motion vector, the motion vector will inaccurately bedetermined in pixels, possibly causing an image quality degradation andoperational failure on each area.

[0027] In a scene that a person 122 moves to the right before astationary window 121 as shown in FIG. 6A, for example, when a motionvector is detected for each of gridironed basic blocks 101, the motionvector of the basic blocks 101 including the person 122 is a rightwardmotion vector 123. On the other hand, the basic blocks 101 not includingthe person 122 will show zero motion vector.

[0028] When a motion correction is done by shifting each block accordingto such a rightward motion vector 123, however, parts (121 a and 121 bin FIG. 6B) of the window 121 also moves correspondingly to the motionof the person 122 as shown in FIG. 6B, resulting in a gap 124. Say, incase pixels forming together a block actually move differently from eachother, a visually unnatural image will result.

SUMMARY OF THE INVENTION

[0029] It is therefore an object of the present invention to overcomethe above-mentioned drawbacks of the related art by suppressingdegradation in quality of a frequency-doubled image by correcting amotion vector of each block of the image, determined by the blockmatching method, to an accurate one of each of the pixels of the image.

[0030] The above object can be attained by providing a motion vectorcorrection circuit which corrects a motion vector determined by theblock matching method, on each of pixels in a basic field that is oneframe before a reference field supplied thereto, the circuit includingaccording to the present invention:

[0031] an edge determining means for determining whether each blockincluding a plurality of pixels extracted from the basic field has anedge or not;

[0032] a stationary/non-stationary-state determining means fordetermining in which state, stationary or non-stationary, each of thepixels forming together one of the blocks which has been determined bythe edge determining means to have an edge is, on the basis of anabsolute value of a difference between the pixel and a pixel in the samepixel position in the reference field;

[0033] a correlation determining means for calculating an absolute valueof a difference between a pixel having been determined by thestationary/non-stationary-state determining means to be non-stationaryand a pixel in each pixel position in the reference field to determine acorrelation between such pixels;

[0034] a peripheral pixel determining means for calculating an absolutevalue of a difference between a pixel on which no correlation is foundand pixels adjacent to the pixel in the basic field to determine acorrelation between the non-correlative pixel and one of the adjacentpixels on the basis of the difference absolute-value thus calculated;and

[0035] a motion vector allocation means for allocating, on each of thepixels, a motion vector determined by the block matching methodaccording to results of the determination made by the edge determiningmeans and stationary/non-stationary-state determining means and in thecorrelation determining means and peripheral pixel determining means.

[0036] Also the above object can be attained by providing a motionvector correction method of correcting a motion vector determined by theblock matching method, on each of pixels in a basic field that is oneframe before an input reference field, the method including, accordingto the present invention, the steps of:

[0037] determining whether each block including a plurality of pixelsextracted from the basic field has an edge or not;

[0038] determining in which state, stationary or non-stationary, each ofthe pixels forming together one of the blocks which has been determinedin the edge determining step to have an edge is, on the basis of anabsolute value of a difference between the pixel and a pixel in the samepixel position in the reference field;

[0039] calculating an absolute value of a difference between a pixelhaving been determined in the stationary/non-stationary-statedetermining step to be non-stationary and a pixel in each pixel positionin the reference field to determine a correlation between such pixels;

[0040] calculating an absolute value of a difference between a pixel onwhich no correlation is found and pixels adjacent to the pixel in thebasic field to determine a correlation between the non-correlative pixeland one of the adjacent pixels on the basis of the differenceabsolute-value thus calculated; and

[0041] allocating, on each of the pixels, a motion vector determined bythe block matching method according to results of the determination madein the edge determining step and stationary/non-stationary-statedetermining step and in the correlation determining step and peripheralpixel determining step.

[0042] In the above motion vector correction circuit and method, it isdetermined whether each block including a plurality of pixels extractedfrom the basic field has an edge or not, it is determined in whichstate, stationary or non-stationary, each of the pixels forming togetherone of the blocks which has been determined by the edge determiningmeans to have an edge is, an absolute value of a difference iscalculated between a pixel having been determined by thestationary/non-stationary-state determining means to be non-stationaryand a pixel in each pixel position in the reference field to determine acorrelation between such pixels, an absolute value of a difference iscalculated between a pixel with which no correlation is found and pixelsadjacent to the pixel in the basic field to determine a correlationbetween the non-correlative pixel and one of the adjacent pixels on thebasis of the difference absolute-value thus calculated, and on each ofthe pixels, there is allocated a motion vector determined by the blockmatching method according to results of the determination.

[0043] These objects and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription of the preferred embodiments of the present invention whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044]FIG. 1 is a block diagram of a field frequency doubler circuithaving the field frequency doubling technique applied therein;

[0045]FIGS. 2A an 2B show the relation between each field and pixelposition before and after subjected to frequency-doubling conversion;

[0046]FIGS. 3A and 3B show the relation between each field and imageposition when an image is shifted horizontally at the time of enteringTV signals;

[0047]FIG. 4 explains an example of motion vector detection in eachblock;

[0048]FIG. 5 shows an example of the construction of the motioncorrection circuit which makes motion correction of a frequency-doubledimage signal;

[0049]FIGS. 6A and 6B shows an example of a person moving before astationary window to the right;

[0050]FIG. 7 is a schematic block diagram of a motion correction system;

[0051]FIG. 8 shows an example of the internal construction of the motionvector correction apparatus according to the present invention;

[0052]FIG. 9 explains the block matching method technique and extendedsearch range;

[0053]FIG. 10 explains the positional relation of a pixel of interestwith pixels adjacent to the pixel of interest;

[0054]FIG. 11 shows a flow of operations made in the motion vectorcorrecting method according to the present invention;

[0055]FIGS. 12A and 12B show an example of the motion vector correctionfor a scene in which a person moving before a stationary window to theright;

[0056]FIG. 13 explains a reallocation flag allocated on every 51 basicblocks according to an edge criterion;

[0057]FIG. 14 explains the reallocation flag allocated on each of thepixels according to each edge criterion;

[0058]FIG. 15 shows a motion vector selected for each of the pixelsaccording to the reallocation flag;

[0059]FIG. 16 shows an example connection of a field frequency doublercircuit to the motion correction system;

[0060]FIGS. 17A and 17B show interlaced image signals before and aftersubjected to frequency-doubling conversion;

[0061]FIGS. 18A and 18B show the relation between each field and imageposition when a frequency-doubled image is shifted horizontally; and

[0062]FIG. 19 shows the result of motion correction of afrequency-doubled image.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0063] The embodiment of the present invention will be describedherebelow with reference to the accompanying drawings.

[0064] The motion vector correction apparatus according to the presentinvention is generally indicated with a reference 1. The motion vectorcorrection apparatus 1 is integrally built in a motion correction system9 used in a TV receiver of, for example, the PAL (phase alternation byline) type.

[0065] Referring now to FIG. 7, there is schematically illustrated inthe form of a block diagram the motion correction system 9. As shown,the motion correction system 9 includes an image memory 61, imageshifter 62 and the motion vector correction apparatus 1 according to thepresent invention.

[0066] The above image memory 61 stores sequentially supplied interlacedimage signals in units of a field for one frame. In the followingexplanation, an image signal output from the image memory 61 will bereferred to as “basic field” 30 hereunder, and an image signal input tothe image memory 61 will be referred to as “reference field” 40hereunder. That is to say, the reference field 40 supplied from theimage memory 61 has a one-frame delay in relation to the basic field 30provided by the image memory 61.

[0067] At each block or pixel, the motion vector correction apparatus 1detects a motion vector based on the supplied basic field 30 andreference field 40, and supplies the image shifter 62 with the detectedmotion vector, namely, information on a magnitude and direction of theshift that are based on the motion vector. The function and compositionof the motion vector correction apparatus 1 will be described in detaillater.

[0068] At each block or pixel, the image shifter 62 receives a motionvector detected by the motion vector correction apparatus 1 orinformation such as magnitude of the shift and the like that are basedon the motion vector. Also, the image shifter 62 shifts each pixelposition or each block in the reference field 40 supplied from the imagememory 61 in the vector direction within the range of the receivedmotion vector. The image shifter 62 supplies the image signal whosepixel position or block has been shifted in the vector direction to aCRT (cathode ray tube) 63 which will display the image signal suppliedfrom the image shifter 62 on the screen thereof.

[0069] The motion vector correction apparatus 1 according to the presentinvention is constructed as will be described below:

[0070] As shown in FIG. 8, the motion vector correction apparatus 1includes a block matching calculator 11, first delay adjuster 12, seconddelay adjuster 13, first shift register 14, edge determination block 15,stationary/non-stationary-state determination block 16, local memory 17,coincidence determination block 18, first line delay block 19, secondshift register 20, correlation determination block 21, reallocation flaggenerator 22, motion vector selector 24, second line delay block 25,third shift register 26 and a motion correction-amount decision block27.

[0071] The block matching calculator 11 detects a motion vector by theblock matching method on the basis of the supplied basic field 30 andreference field 40 as shown in FIG. 9. The block matching calculator 11also detects a block given by an m×n pixel size and having a closestcorrelation with a basic block 51 in the basic field 30 from a searchblock 53 moved within a search range 54 in the reference field 40. Adeviation in position between the detected search block 53 and basicblock 51 (direction and magnitude of the motion) is taken as a motionvector. It should be noted that the pixel size of this search range 54is given by i×j.

[0072] Note that to determine the above correlation, the block matchingcalculator 11 calculates a difference of each pixel value in the searchblock 53 from a pixel value corresponding to the basic block 51 todetermine an assessment value indicated by the difference, for example,a difference absolute-value sum. Next, the block matching calculator 11repeats the above determination with all the search blocks 53 anddetermines a smallest one of the assessment value sums. Next, the blockmatching calculator 11 repeats the above operations for all the searchblocks 53 to determine a smallest one of the assessment value sums, thatis, difference absolute-value sums. Further, the block matchingcalculator 11 takes a search block 53 that provides the smallestdifference absolute-value sum as having the closest correlation with thebasic block 51, and also takes, as a motion vector, a vectoridentifiable between a pixel at the origin of such a block and a one atthe origin of the basic block 51. The block matching calculator 11supplies the detected motion vector to the local memory 17 and motionvector selector 24.

[0073] The first delay adjuster 12 delays the supplied image signal ofthe reference field 40 a time taken for calculation by the blockmatching calculator 11 for example, and supplies the signal thus delayedto the stationary/non-stationary-state determination block 16. Thesecond delay adjuster 13 delays the supplied image signal of the basicfield 30 a time taken for calculation by the block matching calculator11 for example, and supplies the signal thus delayed to the first shiftregister 14. Say, the first and second delay adjusters 12 and 13 work asa so-called delay element.

[0074] The first shift register 14 is supplied with the image signal ofthe basic field 30 from the second delay adjuster 13. The first shiftregister 14 reads the pixel signal level of each pixel (will be referredto as “pixel value” or “value” wherever appropriate hereinafter) fromthe supplied image signal of the basic field 30, and supplies it to theedge determination block 15, stationary/non-stationary-statedetermination block 16, coincidence determination block 18 andcorrelation determination block 21. A pixel read by the first shiftregister 14 is called “pixel of interest” 81. Also, the first shiftregister 14 will read the value of a pixel to the left of the pixel 81and supplies it to the correlation determination block 21. In thefollowing description, a pixel to the left of the pixel of interest 81will be called “left-adjacent pixel” 82. FIG. 10 shows the positionalrelation between the pixel of interest 81 and the left-adjacent pixel 82located to the left of the pixel of interest 81.

[0075] The edge determination block 15 is supplied with the value of thepixel of interest 81 in the basic field 30 from the first shift register14. The edge determination block 15 judges, on the basis of the value ofthe supplied pixel of interest 81, whether each basic block 51 in thebasic block 30 has an edge or not. This judgment of whether each basicblock 51 has an edge can be done by identifying the value of the pixelof interest 81 under the assumption that the pixel of interest 81 iscomposed of pixels forming together the basic block 51. The edgedetermination block 15 generates an edge assessment value “1” for abasic block 51 having been determined have an edge, and supplies thevalue to the reallocation flag generator 22. On the contrary, the edgedetermination block 15 generates an edge assessment value “0” for abasic block 51 having not been determined to have an edge, and suppliesthe value to the reallocation flag generator 22. It should be noted thatthe edge determination block 15 may do this edge determining bycomparison of the pixel of interest 81 with a predetermined threshold.

[0076] The stationary/non-stationary-state determination block 16 issupplied with an image signal of the reference field 40 from the firstdelay adjuster 12 and with the value of the pixel of interest 81 in thebasic field 30 from the first shift register 14. Thestationary/non-stationary-state determination block 16 compares thevalue of the pixel of interest 81 in the basic field 30 with the valueof a pixel in the same pixel position 91 in the reference field 40 asshown in FIG. 10 and judges if the pixel of interest 81 is stationary(will be referred to as “stationary state” hereunder) or moves (will bereferred to as “non-stationary state” hereunder) until the referencefield 40 is reached. In case that the pixel of interest 81 is in thestationary state, the stationary/non-stationary-state determinationblock 16 will generate a stationary/non-stationary-state assessmentvalue “1” and supply it to the reallocation flag generator 22. In casethat the pixel of interest 81 is in the non-stationary state, thestationary/non-stationary-state determination block 16 will generate astationary/non-stationary-state assessment value “0” and supply it tothe reallocation flag generator 22. It should be noted that thestationary/non-stationary-state determination block 16 may do thisdetermination by comparison of an absolute value of a differencecalculated between the value of the pixel of interest 81 and that of thepixel in the pixel position 91 with a predetermined threshold, forexample.

[0077] The local memory 17 is sequentially supplied with the imagesignal of the reference field 40 and also with motion vectors from theblock matching calculator 11. The local memory 17 identifies a pixelposition 92 in the reference field 40, shifted over the motion vectorfrom the pixel of interest 81 as shown in FIG. 10. It should be notedthat the pixel position 92 will be a position shifted over the motionvector from the above pixel position 91 in the reference field 40. Thelocal memory 17 reads the value of a pixel in the pixel position 92 fromeach of the reference fields 40 sequentially written on the basis of themotion vector, and supplies it to the coincidence determination block18.

[0078] The coincidence determination block 18 is supplied with the valueof the pixel of interest 81 in the basic field 30 from the first shiftregister 14, and also with the value of the pixel in the pixel position92 in the reference field 40 from the local memory 17. The coincidencedetermination block 18 compares the value of the pixel of interest 81with the value of the pixel in the pixel position 92 to judge whetherthe pixel of interest 81 has shifted over the motion vector. In casethat the value of the pixel of interest 81 is generally correlated withthe value of the pixel in the pixel position 92, the coincidencedetermination block 18 will determine that the pixel of interest 81 hasshifted over the motion vector, and output a coincidence assessmentvalue “1” to the reallocation flag generator 22. In case that the valueof the pixel of interest 81 is not correlated with the value of thepixel in the pixel position 92, the coincidence determination block 18will determine that the pixel of interest 81 has not shifted over themotion vector, and output a coincidence assessment value “0” to thereallocation flag generator 22. It should be noted that the coincidencedetermination block 18 may do this determination by comparison of anabsolute value of a difference calculated between the value of the pixelof interest 81 and that of the pixel in the pixel position 92 with apredetermined threshold, for example.

[0079] The first line delay block 19 delays the supplied image signal ofthe basic field 30 by one line, for example, and supplies the signal tothe second shift register 20. Owing to the one-line delay made by thefirst line delay block 19 of the image signal of the basic field 30, thevalue of a pixel in a pixel position that is one line above the pixel ofinterest 81 for example can be sent to the second shift register 20.

[0080] The second shift register 20 is supplied with the image signal ofthe basic field 30 from the first line delay block 19. It reads thevalue of each pixel from the supplied image signal of the basic field30, and supplies the pixel value to the correlation determination block21. Say, the second shift register 20 will be sequentially supplied withpixels in pixel positions delayed one line in relation to a line wherethe pixel of interest 81 lies. Thus, in case that the first shiftregister 14 is reading the value of the pixel of interest 81, the valuesof pixels in pixel positions that are one line above the pixel ofinterest 81 can also be read. In the following description, of thepixels one line above the pixel of interest 81, a one to the upper leftof the pixel of interest 81 will be called “upper left-adjacent pixel”83, a one above the pixel of interest 81 be called “upper-adjacentpixel” 84, and a one to the upper right of the pixel of interest 81 becalled “upper right-adjacent pixel” 85, as shown in FIG. 10. The secondshift register 20 reads the value of these upper left-adjacent pixel 83,upper-adjacent pixel 84 and upper right-adjacent pixel 85, respectively,and supplies the values to the correlation determination block 21.

[0081] The correlation determination block 21 is supplied with thevalues of the pixel of interest 81 and left-adjacent pixel 82 from thefirst shift register 14, and also with the values of the upperleft-adjacent pixel 83, upper-adjacent pixel 84 and upper right-adjacentpixel 85 from the second shift register 20. The correlationdetermination block 21 compares the value of the pixel of interest 81with that of the left-adjacent pixel 82, upper left-adjacent pixel 83,upper-adjacent pixel 84 or upper right-adjacent pixel 85 (pixelsadjacent to the pixel of interest 81 and including the pixels 82, 83, 84and 85 will generically be referred to as “adjacent pixel” 8 hereunder)to determine a correlation between the pixel of interest 81 and adjacentpixel 8 on the basis of an absolute value of a difference determinedbetween the values of the pixel of interest 81 and adjacent pixel 8. Thecorrelation determination block 21 finds an adjacent pixel 8 mostcorrelative with the pixel of interest 81 for example, generates acorrelation assessment value, and sends it to the reallocation flaggenerator 22. It is assumed that a correlation assessment value is “1”for a correlation found with the upper left-adjacent pixel 83, “2” for acorrelation found with the upper-adjacent pixel 84, “3” for acorrelation found with the upper right-adjacent pixel 85, and “4” for acorrelation found with the left-adjacent pixel 82. It should be notedthat the correlation determination block 21 may do this determination bycomparison of an absolute value of a difference calculated between thevalue of the pixel of interest 81 and that of the adjacent pixel 8 witha predetermined threshold, for example.

[0082] The reallocation flag generator 22 is supplied with an edgeassessment value from the edge determination block 15, astationary/non-stationary-state assessment value from thestationary/non-stationary-state determination block 16, a coincidenceassessment value from the coincidence determination block 18, and alsowith a correlation assessment value from the coincidence determinationblock 21. The reallocation flag generator 22 generates a reallocationflag on each basic block 51 or pixel on the basis of the suppliedassessment values and following a procedure which will be described indetail later. The reallocation flag generator 22 sends the generatedreallocation flag to the motion vector selector 24.

[0083] The motion vector selector 24 is supplied with a motion vectorfrom the block matching calculator 11, and also with a reallocation flagfrom the reallocation flag generator 22. Further, the motion vectorselector 24 is supplied with a motion vector of the upper left-adjacentpixel 83, upper-adjacent pixel 84 or upper right-adjacent pixel 85 fromthe third shift register 26 which will be described in detail later, andalso with the left-adjacent pixel 82 from itself, the motion vectorselector 24 will allocate an optimum one of the supplied motion vectorsto the pixel of interest 81 according to the supplied reallocation flag,and output the pixel of interest 81 to which the motion vector has thusbeen allocated.

[0084] The output motion vector of the pixel of interest 81 from themotion vector selector 24 is sent to the motion correction-amountdecision block 27, and also fed back to the motion vector selector 24.Since the pixel of interest 81 is sequentially shifted from left toright (in the direction H in FIG. 10) for identification, the outputmotion vector of the pixel of interest 81 is a one for the pixel 82left-adjacent to the pixel of interest 81 identified next to the pixelof interest 81 in consideration.

[0085] Also, the output motion vector of the pixel of interest 81 fromthe motion vector selector 24 is sent to the second line delay block 25.This second line delay block 25 delays the motion vector of the pixel ofinterest 81 to be sent by one line to the third shift register 26.Because of this one-line delay made by the second line delay block 25,it is possible to detect the motion vector of a pixel that is one lineabove the pixel of interest 81.

[0086] The third shift register 26 is supplied with the motion vector ofthe pixel that is one line above the pixel of interest 81 from thesecond line delay block 25. The third shift register 26 will extract themotion vectors of the upper left-adjacent pixel 83, upper-adjacent pixel84 and upper right-adjacent pixel 85 from the supplied motion vector ofthe one-line above pixel. Also, the third shift register 26 outputs themotion vectors of the upper left-adjacent pixel 83, upper-adjacent pixel84 and upper right-adjacent pixel 85 to the motion vector selector 24.

[0087] The motion correction-amount decision block 27 is supplied with amotion vector allocated on each of the pixels from the motion vectorselector 24. The motion correction-amount decision block 27 converts themotion vector into an appropriate shift amount for a motion on the basisof the motion vector allocated on each of the pixels, and outputs theshift amount to an output terminal 28.

[0088] Next, the motion vector correction apparatus 1 according to thepresent invention functions as will be described with reference to theflow chart in FIG. 11.

[0089]FIG. 12A shows an image whose motion vector is to be corrected foreach of the pixels in the procedure shown in FIG. 11. FIG. 12A shows apart, defined by a thick frame, in an enlarged scale, of a scene inwhich a person 152 moves to the right before a window 151 as shown inFIG. 12B. In the partial scene, the basic block 51 is gridironed in thebasic field 30. In the example shown in FIG. 12A, the basic block 51including basic blocks 51A to 51I in this order from the left iscomposed of eight pixels by two lines, and positions of the pixelsforming together each basic block 51 are represented by lines O to T androws 1 to 24 in this order from the upper-left pixel position.

[0090] Note that in FIG. 12A, the window 151 is depicted in the rows 8to 13 and the person 152 is depicted to the upper right from the pixelposition defined by the line T and row 12. The person 152 moves overseven pixels to the left in the reference field 40. Say, the motionvector determined for the person 152 has a magnitude of seven pixels andthe vector direction is rightward.

[0091] In the motion vector correction apparatus 1, the edgedetermination block 15 judges in step S11 in FIG. 11 whether each of thebasic blocks 51A to 51I has an edge or not. This judgment is done bydetecting a pixel of interest 81 for each of the basic blocks 51 andassessing the pixel value of the detected pixel of interest 81. Sincethe basic blocks 51F and 51I of the basic blocks 51A to 51I are composedof the person 152 alone, the edge determination block 15 will not beable to detect any edge of these basic blocks 51F and 51I. Therefore,all the pixels of interest 81 included in the basic block 51 have thesame value. Thus, the edge determination block 15 will go to step S12with generation of an edge assessment value “0” for the basic blocks 51Fand 51I.

[0092] On the contrary, since the edge determination block 15 determinesin step S11, that the basic blocks 51 other than the above basic blocks51F and 51I have an edge and the pixels of interest 81 forming togetherthe basic blocks 51 have values different from each other, it will go tostep S21 with generation of an edge assessment value “1”.

[0093] In step S12, the reallocation flag generator 22 generates areallocation flag on each basic block 51 according to the edgeassessment value sent from the edge determination block 15. In thiscase, the reallocation flag generator 22 allocates a reallocation flag“N” on the basic blocks 51F and 51I for which the edge assessment value“0” is generated, as shown in FIG. 13. Also, the reallocation flaggenerator 22 allocates a reallocation flag “P” on the basic blocks 51for which the edge assessment value “1” is generated, as shown in FIG.13.

[0094] That is, first in steps S11 to S12, the motion vector correctionapparatus 1 according to the present invention can determine a motionvector as usual by detecting a motion vector on each block andallocating different reallocation flags to motion vectors of the basicblocks having no edge. Thus, for the blocks having no edge, in otherwords, for uni-colored blocks, the motion vector has not to be correctedfor each of the pixels, which enables to reduce the operational amountof the apparatus.

[0095] Note that for the basic blocks 51 on which the reallocation flag“P” is allocated as shown in FIG. 13, a motion vector is allocated oneach of the pixels in step S21 and subsequent steps.

[0096] In step S21, the stationary/non-stationary-state determinationblock 16 judges in which state, stationary or non-stationary, each ofthe pixels in the basic blocks 51 on which the reallocation flag “P” isallocated is. On the assumption that the pixel value of the pixel ofinterest 81 in the basic field 30 is g(m, n, t) and the pixel value of apixel in the pixel position 91 in the reference field 40 is g(m, n, t+1)as shown in FIG. 10, the stationary/non-stationary-state determinationblock 16 will make a comparison between a calculated differenceabsolute-value and a threshold, as given by the following expression(21) for example:

|g(m, n, t)−g(m, n, t+1)|<Threshold α  (21)

[0097] When the expression (21) is satisfied, namely, when the termsg(m, n, t) and g(m, n, t+1) are nearly equal to each other, it issuggested that the pixel of interest 81 remains stationary until thereference field 40 is reached, and the stationary/non-stationary-statedetermination block 16 will go to step S22 with generation of astationary/non-stationary-state assessment value “1”. In this case,since the pixels forming together the window 151 are stationary, thestationary/non-stationary-state assessment value “1” is generated forthe pixels.

[0098] On the contrary, when the expression (21) is not satisfied, inother words, when the terms g(m, n, t) and g(m, n, t+1) are notcorrelated with each other, it is suggested that the pixel of interest81 is moved until the reference field 40 is reached, and thestationary/non-stationary-state determination block 16 will go to stepS31 with generation of a stationary/non-stationary-state assessmentvalue “0”.

[0099] In step S22, the reallocation flag generator 22 allocates areallocation flag on each pixel of interest 81 on the basis of astationary/non-stationary-state assessment value sent from thestationary/non-stationary-state determination block 16. In this case, areallocation flag “S” is allocated on each of the pixels formingtogether the window 151 for example, as shown in FIG. 14.

[0100] As shown in FIG. 14, the pixel of interest 81 causing thestationary/non-stationary-state determination block 16 to go to stepS31, namely, the pixel of interest 81 on which thestationary/non-stationary-state assessment value “0” has been allocatedin step S21, is a pixel forming the person 152 and included in the basicblock 51 having an edge or a pixel forming other than the person 152 andwhich does not strictly satisfy the expression (21) because it islocated near the person 152. In step S31, of such pixel of interest 81,ones are identified which evidently form together the person 152.

[0101] In step S31, the coincidence determination block 18 will judgewhether the pixel of interest 81 has shifted over the motion vector bymaking a comparison between the pixel value of the pixel of interest 81for which the stationary/non-stationary-state assessment value “0” hasbeen generated and that of a pixel in the pixel position 92 for thepixel of interest 81. Thereby, the pixel of interest 81 forming theperson 152 can be identified.

[0102] On the assumption that the pixel value of the pixel in the pixelposition 92 shifted over a motion vector (Vx, Vy) from the pixelposition 91 in the reference field 40 is g(m+Vx, n+Vy, t+1) as shown inFIG. 10, the coincidence determination block 18 will make a comparisonbetween the calculated difference absolute-value and threshold as givenby the following expression (22) for example:

|g(m, n, t)−g(m+Vx, n+Vy, t+1)|<Threshold β  (22)

[0103] When the expression (22) is satisfied, namely, when the termsg(m, n, t) and g(m+Vx, n+Vy, t+1) are nearly equal to each other, it issuggested that the pixel of interest 81 has shifted over the motionvector until the reference field 40 is reached, and the coincidencedetermination block 18 will go to step S32 with generation of acoincidence assessment value “1”. In this case, since the pixels formingtogether the person 152 move over the motion vector, the coincidenceassessment value “1” is generated for the pixels. On the contrary, whenthe expression (22) is not satisfied, in other words, when the termsg(m, n, t) and g(m+Vx, n+Vy, t+1) are not correlated with each other, itis suggested that the pixel of interest 81 is moved until the referencefield 40 is reached, and the coincidence determination block 18 will goto step S41 with generation of a coincidence assessment value “0”.

[0104] In step S32, the reallocation flag generator 22 allocates areallocation flag on each pixel of interest 81 on the basis of acoincidence assessment value sent from the coincidence determinationblock 18. In this case, a reallocation flag “M” is allocated to each ofthe pixels forming together the person 152 for example, as shown in FIG.14.

[0105] The pixel of interest 81 causing the coincidence determinationblock 18 to go to step S41, namely, the pixel of interest 81 to whichthe coincidence assessment value “0” has been allocated in step S31, isa pixel forming the person 152 or a pixel forming other than the person152 and which does not strictly satisfy the expression (22) because itis located near the person 152. In step S41, such pixel of interest 81between the stationary image and non-stationary one is adapted to anadjacent pixel 8 showing a highest correlation.

[0106] On the assumption that the pixel value of the left-adjacent pixel82 is g(m−1, n, t) and that of the left upper-adjacent pixel 83 is g(m−1, n+1, t) as shown in FIG. 10, that of the upper-adjacent pixel 84is g(m, n+1, t) and that of the right upper-adjacent pixel 85 is g(m+1,n+1, t) as shown in FIG. 10, the correlation determination 21 makesfirst a comparison between the pixel value g(m, n, t) of the pixel ofinterest 81 and the pixel value g(m−1, n+1, t) of the leftupper-adjacent pixel 83 on the basis of the following expression (23)for example:

|g(m, n, t)−g(m−1n+1, t)|<Threshold γ  (23)

[0107] When the expression (23) is satisfied, namely, when the termsg(m, n, t) and g(m−1, n+1, t) are nearly equal to each other, it issuggested that the pixel of interest 81 is correlated with the leftupper-adjacent pixel 83. In this case, the correlation determinationblock 21 will go to step S51 with generation of a correlation assessmentvalue “1”.

[0108] On the contrary, when the expression (23) is not satisfied, it issuggested that the pixel of interest 81 is not correlated with the leftupper-adjacent pixel 83. In this case, the correlation determinationblock 21 will make a comparison between the pixel value g(m, n, t) ofthe pixel of interest 81 and the pixel value g(m, n+1, t) of theupper-adjacent pixel 84 on the basis of the following expression (24)for example:

|g(m, n, t)−g(m, n+1, t)|<Threshold γ  (24)

[0109] When the expression (24) is satisfied, namely, when the termsg(m, n, t) and g(m, n+1, t) are nearly equal to each other, it issuggested that the pixel of interest 81 is correlated with theupper-adjacent pixel 84. In this case, the correlation determinationblock 21 will go to step S52 with generation of a correlation assessmentvalue “2”.

[0110] On the contrary, when the expression (24) is not satisfied, it issuggested that the pixel of interest 81 is not correlated with theupper-adjacent pixel 84. In this case, the correlation determinationblock 21 will make a comparison between the pixel value g(m, n, t) ofthe pixel of interest 81 and the pixel value g(m+1, n+1, t) of the rightupper-adjacent pixel 85 on the basis of the following expression (25)for example:

|g(m, n, t)−g(m+1, n+1, t)|<Threshold γ  (25)

[0111] When the expression (25) is satisfied, namely, when the termsg(m, n, t) and g(m+1, n+1, t) are nearly equal to each other, it issuggested that the pixel of interest 81 is correlated with the rightupper-adjacent pixel 85. In this case, the correlation determinationblock 21 will go to step S53 with generation of a correlation assessmentvalue “3”.

[0112] On the contrary, when the expression (25) is not satisfied, it issuggested that the pixel of interest 81 is not correlated with the rightupper-adjacent pixel 85. In this case, the correlation determinationblock 21 will make a comparison between the pixel value g(m, n, t) ofthe pixel of interest 81 and the pixel value g(m−1, n, t) of the letadjacent pixel 82 on the basis of the following expression (26) forexample:

|g(m, n, t)−g(m−1, n, t)|<Threshold γ  (26)

[0113] When the expression (26) is satisfied, namely, when the termsg(m, n, t) and g(m−1, n, t) are nearly equal to each other, it issuggested that the pixel of interest 81 is correlated with theleft-adjacent pixel 82. In this case, the correlation determinationblock 21 will go to step S54 with generation of a correlation assessmentvalue “4”.

[0114] On the contrary, when the expression (26) is not satisfied, it issuggested that the pixel of interest 81 is not correlated with theleft-adjacent pixel 82. In this case, the correlation determinationblock 21 will got to step S55 with generation of a correlationassessment value “0”.

[0115] Namely, in step S41, the correlation determination block 21 makesa comparison of the left upper-adjacent pixel 83, upper-adjacent pixel84, fight upper adjacent-pixel 85 and left-adjacent pixel 82, in thisorder, with the pixel of interest 81. In case that each of thedifference between the pixels in comparison is smaller than thethreshold γ, the correlation determination block 21 will go to steps S51to S55. In other words, the comparison, for correlation determination,with the pixel of interest 81 is done preferentially starting with theleft upper-adjacent pixel 83.

[0116] Note that step S41 is not limited to the aforementioned procedureand method but the order of adjacent pixels 8 to be compared in pixelvalue with the pixels of interest 81 may be changed and also thecomparison, for correlation determination, with the pixel of interest 81may be done preferentially starting with the upper-adjacent pixel 84,right upper-adjacent pixel 85 or left-adjacent pixel 82 as well asstarting with the left upper-adjacent pixel 83.

[0117] Also, for the correlation determination in step S41, the pixel ofinterest 81 is compared with the four pixels including the leftupper-adjacent pixel 83, upper-adjacent pixel 84, right upper-adjacentpixel 85 and left-adjacent pixel 82 of the adjacent pixels 8. However,the present invention is not limited to this method, but for the samepurpose, the pixel of interest 81 may be compared with all adjacentpixels such as pixels right-adjacent thereto, lower-adjacent thereto,etc. Also, in step S41, for the correlation determination, the pixel ofinterest 81 may be compared with other than the adjacent pixels 8, suchas pixels that are one pixel or two pixels apart from the pixel ofinterest 81.

[0118] Further, for the same purpose in step S41, the pixel of interest81 may be compared with one of the adjacent pixels 8, whose absolutevalue of a difference in pixel value from the pixel of interest 81 isminimum. Thereby, it is possible to select an adjacent pixel 8 whosepixel value is nearest to that of the pixel of interest 81 and to adaptthat pixel to the surrounding image.

[0119] In step S51, the reallocation flag generator 22 generates areallocation flag “A” on a pixel of interest 81 to which the correlationassessment value “1” has been allocated by the correlation determinationblock 21.

[0120] In step S52, the reallocation flag generator 22 generates areallocation flag “B” on a pixel of interest 81 to which the correlationassessment value “2” has been allocated by the correlation determinationblock 21.

[0121] In step S53, the reallocation flag generator 22 generates areallocation flag “C” on a pixel of interest 81 to which the correlationassessment value “3” has been allocated by the correlation determinationblock 21.

[0122] In step S54, the reallocation flag generator 22 generates areallocation flag “D” on a pixel of interest 81 to which the correlationassessment value “4” has been allocated by the correlation determinationblock 21.

[0123] In step S55, the reallocation flag generator 22 generates areallocation flag “E” on a pixel of interest 81 to which the correlationassessment value “0” has been allocated by the correlation determinationblock 21.

[0124] In step S51 to S55, a reallocation flag generated on each pixelof interest 81 is allocated to pixels of interest 81 lying between astationary image such as the window 151 and a non-stationary image suchas the person 152 as shown in FIG. 14. For example, a reallocation flag“C” is allocated on a pixel of interest 81 lying at an 3intersection ofthe line T and row 12. Say, it is suggested that the pixel at theintersection between the line T and row 12 are highly correlative with aright upper-adjacent pixel at an intersection between the line S and row13. Also, a reallocation flag “D” is allocated on a pixel of interest 81lying at an intersection between the line Q and row 15. Say, it issuggested that the pixel at the intersection between the line Q and row15 is highly correlative with the pixel at a left-adjacent pixel at anintersection between the line Q and row 14. As shown in FIG. 14, after areallocation flag is allocated on each of all the pixels, the motionvector correction apparatus 1 goes to step S61.

[0125] In step S61, the motion vector selector 24 will select a motionvector according to the reallocation flag allocated on each of thepixels. When the reallocation flag is “S”, the motion vector (Vx, Vy) istaken as (0, 0). Also, in case the reallocation flag is “A”, the motionvector selector 24 will select the motion vector of the leftupper-adjacent pixel 83. In case the reallocation flag is “B”, themotion vector selector 24 will select the motion vector of theupper-adjacent pixel 84. In case the reallocation flag is “C”, themotion vector selector 24 will select the motion vector of the leftupper-adjacent pixel 83. In case the reallocation flag is “D”, themotion vector selector 24 will select the motion vector of theleft-adjacent pixel 82. Further, in case the reallocation flag is “M”,“N” or “E”, the motion vector selector 24 will select a motion vectordetermined by the block matching calculator 11 as it is.

[0126] The result of motion vector selection made according to theallocated reallocation flags as shown in FIG. 14 is shown in FIG. 15. InFIG. 15, “0” stated in the place of each pixel means that the motionvector (Vx, Vy) is (0, 0). Also, “7” means that the motion vector (Vx,Vy) is (0, 7). Namely, it will be seen that there has been correctlyselected a motion vector indicating that each of the pixels included inthe image of the person 152 moves over seven pixels to the left.

[0127] Since the motion vector correction apparatus 1 according to thepresent invention can correct a motion vector in blocks, determined bythe block matching method, to an accurate motion vector in pixels evenif pixels forming together a block move differently from each other, soit is possible to prevent a frequency-doubled image from being degradedin quality.

[0128] Especially, since the motion vector correction apparatus 1 canfirst correct a motion vector in units of a block and then correct themotion vector in units of a pixel in steps S11 and S12, it can make themotion vector correction with a considerably reduced amount of operationas compared with the determination of a motion vector on each of allpixels by the block matching method. Also, since the motion vectorcorrection apparatus 1 can allocate a reallocation flag on each pixelaccording to the results of determination by thestationary/non-stationary-state determination block 16 and coincidencedetermination block 18 and also can determine, by means of thecorrelation determination block 21, a correlation of adjacent pixels 8lying at the boundary between a stationary image and non-stationaryimage, where the correlation determination is difficult, with a pixel ofinterest, so it can make the motion vector correction with aconsiderably reduced amount of operation and an improved accuracy.

[0129] Note that the present invention is not limited to theaforementioned embodiment. For example, the interlaced image signalsupplied to the aforementioned motion correction system 9 may be asignal converted by the field frequency doubler circuit 260 to have adouble field frequency. The field frequency doubler circuit 260 isprovided to prevent the screen flicker by improving the resolution. Forexample, in the PAL system, the field frequency doubler circuit 260converts an image signal whose field frequency is 50 Hz into a one whosefield frequency is 100 Hz by a processing such as an interpolation orthe like.

[0130] The field frequency doubler circuit 260 includes an inputterminal 261 connected to a TV receiver, frequency doubler circuit 262and a frame memory 263 as shown in FIG. 16.

[0131] The frequency doubler circuit 262 is supplied withtelecine-converted image signal from the TV receiver via the inputterminal 261 and writes the signal into the frame memory 263. Thefrequency doubler circuit 262 reads the image signal once written to theframe memory 263 at a speed double that at which the signal has beenwritten. Thus, the frequence of image signal of a film image of 50fields/sec in the PAL system is doubled. That is, image signal of 100fields/sec can be reproduced. The frequency doubler circuit 262 sendsthe double-frequency image signal to the motion correction system 9.

[0132]FIGS. 17A and 17B show the relation between each field before andafter subjected to frequency doubling in the field frequency doublercircuit 260 and the pixel position. In FIGS. 17A and 17B, the horizontalaxis indicates a time, while the vertical axis indicates a verticalposition of a pixel.

[0133] The image signal before being frequency-doubled is interlacedimage signal of 50 fields/sec in the PAL and forms one frame from twofields thereof as shown in FIG. 17A.

[0134] On the other hand, since the frequency-doubled image signal is a100-fields/sec interlaced one, two fields t2′ and t1′ are newly producedbetween the fields t1 and t2 and two fields t4′ and t3′ are also newlyproduced between the fields t3 and t4 without generation of any fieldsbetween the fields t2 and t3. Say, in the image signal, one frame willbe formed from four fields.

[0135] Each of the newly formed fields t1′, t2′, . . . may have its ownpixel value determined as a mean value, respectively, of three pixelssurrounding-that pixel by a median filter or the like in some cases asshown in FIG. 17B. Also, the new fields t1′, t2′, . . . will have thesame contents as the fields t1, t2, . . . , respectively. With thenumber of screens per unit time thus increased, four fields will formone frame, and the resolution can be improved and screen flicker can besuppressed.

[0136]FIG. 18A shows the relation between each field and pixel positionin case that image signal in which one frequency-doubled frame is formedfrom four fields is shifted horizontally by the motion correction system9. In FIG. 18A, the horizontal axis indicates a horizontal position ofan image, while the vertical axis indicates a time. An image whose fieldfrequency has already been double is supplied in the sequence of fieldst1, t2′, t1′ and t2 to the image memory 61 at constant time intervals.The fields t1 and t2′ have pixels in the same position, and also thefields t1′ and t2 have pixels in the same position.

[0137] The motion vector correction apparatus 1 determines a motionvector between these fields (frames) as above. As shown in FIG. 18B forexample, when the quantity of a motion vector determined between thefields t1 and t1′ is A, the image shifter 62 will shift the field t2′ inan intermediate position between the fields t1 and t1′ by A/2. Also,when the quantity of a determined motion vector between the subsequentfields is B, the image shifter 62 will also shift the intermediate fieldby B/2.

[0138] Repeating the above operations, an image whose frequency-doubledframe is composed of four fields as shown in FIG. 19 can shown asmoother motion.

[0139] In case that a motion vector determined by the block matchingmethod is outside a search range, the motion vector correction apparatus1 according to the present invention can correct the motion vector sothat it will match a real image motion. So, by doubling the fieldfrequency of image signal, it is possible to move an image moresmoothly, reduce the image quality degradation. These effects incombination will assure the user of quality images.

[0140] Also, the present invention is not limited to the embodimenthaving been illustrated and explained in the foregoing but can of coursebe applied to a signal converter or the like which is used in connectionwith a TV receiver, for example. Also the motion vector detectoraccording to the present invention cannot only be implemented as acircuit, hardware or the like but also as a software in a processor.

[0141] In the foregoing, the present invention has been described indetail concerning certain preferred embodiments thereof as examples withreference to the accompanying drawings. However, it should be understoodby those ordinarily skilled in the art that the present invention is notlimited to the embodiments but can be modified in various manners,constructed alternatively or embodied in various other forms withoutdeparting from the scope and spirit thereof as set forth and defined inthe appended claims.

[0142] As having been described in the foregoing, in the motion vectorcorrection apparatus and method according to the present invention, itis determined whether each block including a plurality of pixelsextracted from a basic field has an edge or not, it is determined inwhich state, stationary or non-stationary, each of the pixels in a blockdetermined to have an edge is, it is determined, on the basis of anabsolute value of a difference calculated between a pixel determined tobe in the non-stationary state and a pixel in each pixel position in areference field or an adjacent pixel, if the pixel is correlated withthe non-stationary pixel or adjacent pixel, and a motion vectordetermined by the block matching method according to results of thedetermination is allocated to each pixel.

[0143] Since the motion vector correction apparatus and method accordingto the present invention can accurately correct a motion vector of eachpixel even in case pixels included in a block move differently from eachother, so it is possible to prevent a frequency-doubled image from beingdegraded in quality. Also, since the motion vector correction apparatusand method can correct the motion vector in units of a block, and thenin units of a pixel, so it can correct the motion vector with aconsiderably reduced amount of operation as compared with the motionvector determination of all pixels by the block matching method.Further, since the motion vector correction apparatus and method cancorrect the motion vector with a high accuracy even with pixels in anarea where the correlation determination is not easy, such as boundarybetween a stationary image and non-stationary image by allocating areallocation flag on each of the pixels according to results ofdetermination by the stationary/non-stationary-state determination blockand coincidence determination block.

What is claimed is:
 1. A motion vector correction circuit which correctsa motion vector determined by the block matching method, on each ofpixels in a basic field that is one frame before a reference fieldsupplied thereto, the circuit comprising: an edge determining means fordetermining whether each block including a plurality of pixels extractedfrom the basic field has an edge or not; astationary/non-stationary-state determining means for determining inwhich state, stationary or non-stationary, each of the pixels formingtogether one of the blocks which has been determined by the edgedetermining means to have an edge is, on the basis of an absolute valueof a difference between the pixel and a pixel in the same pixel positionin the reference field; a correlation determining means for calculatingan absolute value of a difference between a pixel having been determinedby the stationary/non-stationary-state determining means to benon-stationary and a pixel in each pixel position in the reference fieldto determine a correlation between such pixels; a peripheral pixeldetermining means for calculating an absolute value of a differencebetween a pixel on which no correlation is found and pixels adjacent tothe pixel in the basic field to determine a correlation between thenon-correlative pixel and one of the adjacent pixels on the basis of thedifference absolute-value thus calculated; and a motion vectorallocation means for allocating, to each of the pixels, a motion vectordetermined by the block matching method according to results of thedetermination made by the edge determining means andstationary/non-stationary-state determining means and by the correlationdetermining means and peripheral pixel determining means.
 2. The circuitas set forth in claim 1, further comprising a motion vector detectingmeans for determining, by the block matching method, the motion vectorbetween a block extracted from the basic field and a block extractedfrom the reference field and moved within a search range.
 3. The circuitas set forth in claim 1, further comprising a flag generating means forgenerating a flag on each of the pixels according to results of thedetermination made by the edge determining means andstationary/non-stationary-state determining means and by the correlationdetermining means and peripheral pixel determining means; wherein themotion vector allocation means allocates the motion vector on each ofthe pixels according to a flag generated by the flag generating means.4. The circuit as set forth in claim 1, wherein thestationary/non-stationary-state determining means determines that eachof pixels forming together a block determined to have an edge isstationary in case that the calculated difference absolute-value issmaller than a predetermined threshold.
 5. The circuit as set forth inclaim 1, wherein the correlation determining means finds the correlationbetween the pixels in case that the calculated difference absolute-valueis smaller than a predetermined threshold.
 6. The circuit as set forthin claim 1, wherein the peripheral pixel determining means determinesthe correlation on one of the adjacent pixels whose differenceabsolute-value is minimum.
 7. The circuit as set forth in claim 1,wherein the peripheral pixel determining means calculates a differenceabsolute-value between the non-correlative pixel and left upper, upper,right upper and left pixels adjacent to the non-correlative pixel todetermine a correlation on the non-correlative pixel with the adjacentpixel in case that the calculated difference absolute-value is smallerthan a predetermined threshold.
 8. The circuit as set forth in claim 1,wherein the motion vector allocation means operates to: allocate thedetermined motion vector to the blocks having been determined by theedge determining means to have no edge; take, as zero, the motion vectorof a pixel having been determined by the stationary/non-stationary-statedetermining means to be stationary; allocate the determined motionvector to a pixel having been determined by the correlation determiningmeans to have a correlation with one of its adjacent pixels; andallocate the motion vector of one of the adjacent pixels determined tohave the correlation, as it is, to the pixel having been determined bythe peripheral pixel determining means to have a correlation with thenon-correlative pixel.
 9. A motion vector correction method ofcorrecting a motion vector determined by the block matching method, oneach of pixels in a basic field that is one frame before an inputreference field, the method comprising the steps of: determining whethereach block including a plurality of pixels extracted from the basicfield has an edge or not; determining in which state, stationary ornon-stationary, each of the pixels forming together one of the blockswhich has been determined in the edge determining step to have an edgeis, on the basis of an absolute value of a difference between the pixeland a pixel in the same pixel position in the reference field;calculating an absolute value of a difference between a pixel havingbeen determined in the stationary/non-stationary-state determining stepto be non-stationary and a pixel in each pixel position in the referencefield to determine a correlation between such pixels; calculating anabsolute value of a difference between a pixel on which no correlationis found and pixels adjacent to the pixel in the basic field todetermine a correlation between the non-correlative pixel and one of theadjacent pixels on the basis of the difference absolute-value thuscalculated; and allocating, to each of the pixels, a motion vectordetermined by the block matching method according to results of thedetermination made in the edge determining step andstationary/non-stationary-state determining step and in the correlationdetermining step and peripheral pixel determining step.
 10. The methodas set forth in claim 9, further comprising a motion vector detectingstep for determining, by the block matching method, the motion vectorbetween a block extracted from the basic field and a block extractedfrom the reference field and moved within a search range.
 11. The methodas set forth in claim 9, further comprising a flag generating step forgenerating a flagon each of the pixels according to results of thedetermination made in the edge determining step andstationary/non-stationary-state determining step and in the correlationdetermining step and peripheral pixel determining step; wherein, in themotion vector allocation step, the motion vector is allocated on each ofthe pixels according to a flag generated by the flag generating means.12. The method as set forth in claim 9, wherein, in thestationary/non-stationary-state determining step, it is determined thateach of pixels forming together a block determined to have an edge isstationary in case that the calculated difference absolute-value issmaller than a predetermined threshold.
 13. The method as set forth inclaim 9, wherein, in the correlation determining step, there is foundthe correlation between the pixels in case that the calculateddifference absolute-value is smaller than a predetermined threshold. 14.The method as set forth in claim 9, wherein, in the peripheral pixeldetermining step, there is found the correlation on one of the adjacentpixels whose difference absolute-value is minimum.
 15. The method as setforth in claim 9, wherein, in the peripheral pixel determining step,there is calculated a difference absolute-value between thenon-correlative pixel and left upper, upper, right upper and left pixelsadjacent to the non-correlative pixel to determine a correlation on thenon-correlative pixel with the adjacent pixel in case that thecalculated difference absolute-value is smaller than a predeterminedthreshold.
 16. The method as set forth in claim 9, wherein, in themotion vector allocation step: the determined motion vector is allocatedto the blocks having been determined by the edge determining means tohave no edge; the motion vector of a pixel having been determined by thestationary/non-stationary-state determining means to be stationary istaken as zero; the determined motion vector is allocated to a pixelhaving been determined by the correlation determining means to have acorrelation with one of its adjacent pixels; and the motion vector ofone of the adjacent pixels, determined to have the correlation, isallocated as it is to the pixel having been determined by the peripheralpixel determining means to have a correlation with the non-correlativepixel.